If they are to be interchangeable while also being paralleled they have to have very nearly exactly the same reactance or they won't share power evenly and there will be circulating currents between the transformers wasting energy.
Keeping a stock of million dollar items in case one fails once in fifty years is pretty poor use of capital. By the time you get to use it the standards will have changed. And how many different transformers will you keep in stock> You can't reasonably use 500 MVA transformers everywhere, some places only need a 250 MVA unit and might not have space for anything larger. Which voltages will you choose and what will you do with your 500 kV transformer when the backbone gets upgraded to 650 kV or 750 kV or 1 MV?
Do you think that the people who run electricity distribution systems don't think of these things?
php is the only popular language that regularly removes insane legacy cruft (to be fair, they have more insane cruft than almost any other language to begin with).
Real men know that infinite sets are just a tool for proving statements in Peano arithmetic, and complex numbers must be endowed with the standard metric structure, as God intended, since otherwise we cannot use them to approximate IEEE 754 floats.
Counting warnings is a poor practice, because you don't see where warnings exist or are added or removed while reading or writing code. Suppression annotations in code next to where the problem occurs are more explicit, and the progress is easy to measure with e.g. git log -S. The main difficulty is automating adding these annotations. For at least one static analysis systems, there is an off the shelf solution: https://github.com/palantir/suppressible-error-prone
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